TStringEditLink 被销毁后访问冲突（TVirtualStringTree）- Lazarus 示例

Question

我尝试基于 Lazarius

的 example 为 VirtualStringTree 实现一个编辑器

你能告诉我为什么 TStringEditLink 被销毁后我会遇到访问冲突吗？

奇怪的是，只有当我按 ESCAPE 或 ENTER 时才会出现错误。如果我从一个单元格单击到另一个单元格，则没有错误。

就像观察一样，我发现如果我从 destructor TStringEditLink.Destroy 中删除 FEdit.Free 代码，错误就会消失。

你有解决办法吗？

完整代码如下：

unit Unit2;

interface

uses
  Winapi.Windows, Winapi.Messages, System.SysUtils, System.Variants, System.Classes, Vcl.Graphics,
  Vcl.Controls, Vcl.Forms, Vcl.Dialogs, VirtualTrees, EditorLink, Vcl.StdCtrls,
  Vcl.ExtCtrls, Vcl.Imaging.jpeg;

type
  TTreeData = record
    Fields: array of String;
  end;
  PTreeData = ^TTreeData;

const
  SizeVirtualTree = SizeOf(TTreeData);

type
  TForm2 = class(TForm)
    VirtualTree: TVirtualStringTree;
    procedure FormCreate(Sender: TObject);
    procedure VirtualTreeClick(Sender: TObject);
    procedure VirtualTreeCreateEditor(Sender: TBaseVirtualTree;
      Node: PVirtualNode; Column: TColumnIndex; out EditLink: IVTEditLink);
    procedure VirtualTreeEditing(Sender: TBaseVirtualTree; Node: PVirtualNode;
      Column: TColumnIndex; var Allowed: Boolean);
    procedure VirtualTreeFreeNode(Sender: TBaseVirtualTree; Node: PVirtualNode);
    procedure VirtualTreeGetNodeDataSize(Sender: TBaseVirtualTree;
      var NodeDataSize: Integer);
    procedure VirtualTreeGetText(Sender: TBaseVirtualTree; Node: PVirtualNode;
      Column: TColumnIndex; TextType: TVSTTextType; var CellText: string);
    procedure VirtualTreeNewText(Sender: TBaseVirtualTree; Node: PVirtualNode;
      Column: TColumnIndex; NewText: string);
  private
    { Private declarations }
  public
    { Public declarations }
  end;

var
  Form2: TForm2;

implementation

{$R *.dfm}

procedure TForm2.FormCreate(Sender: TObject);
var
  Node: PVirtualNode;
  LTreeData: PTreeData;
begin
  VirtualTree.Clear;
  VirtualTree.BeginUpdate;

  //node 1
  Node:= VirtualTree.AddChild(nil,nil);
  VirtualTree.ValidateNode(Node,False);

  LTreeData:= VirtualTree.GetNodeData(Node);
  SetLength(LTreeData^.Fields,3);

  LTreeData^.Fields[0]:= 'John';
  LTreeData^.Fields[1]:= '2500';
  LTreeData^.Fields[2]:= 'Production';

  //node 2
  Node:= VirtualTree.AddChild(nil,nil);
  VirtualTree.ValidateNode(Node,False);

  LTreeData:= VirtualTree.GetNodeData(Node);
  SetLength(LTreeData^.Fields,3);

  LTreeData^.Fields[0]:= 'Mary';
  LTreeData^.Fields[1]:= '2100';
  LTreeData^.Fields[2]:= 'HR';

  VirtualTree.EndUpdate;
end;

procedure TForm2.VirtualTreeClick(Sender: TObject);
var
  VT: TVirtualStringTree;
  Click: THitInfo;
begin
  VT:= Sender as TVirtualStringTree;
  VT.GetHitTestInfoAt(Mouse.CursorPos.X-VT.ClientOrigin.X, Mouse.CursorPos.Y-VT.ClientOrigin.Y, True, Click);
  VT.EditNode(Click.HitNode,Click.HitColumn);
end;

procedure TForm2.VirtualTreeCreateEditor(Sender: TBaseVirtualTree;
  Node: PVirtualNode; Column: TColumnIndex; out EditLink: IVTEditLink);
begin
  EditLink := TStringEditLink.Create;
end;

procedure TForm2.VirtualTreeEditing(Sender: TBaseVirtualTree;
  Node: PVirtualNode; Column: TColumnIndex; var Allowed: Boolean);
begin
  Allowed:= True;
end;

procedure TForm2.VirtualTreeFreeNode(Sender: TBaseVirtualTree;
  Node: PVirtualNode);
var
  LTreeData: PTreeData;
begin
  LTreeData:= Sender.GetNodeData(Node);
  Finalize(LTreeData^);
end;

procedure TForm2.VirtualTreeGetNodeDataSize(Sender: TBaseVirtualTree;
  var NodeDataSize: Integer);
begin
  NodeDataSize:= SizeVirtualTree;
end;

procedure TForm2.VirtualTreeGetText(Sender: TBaseVirtualTree;
  Node: PVirtualNode; Column: TColumnIndex; TextType: TVSTTextType;
  var CellText: string);
var
  LTreeData: PTreeData;
begin
  if Assigned(Node) and (Column > NoColumn) then
    begin
      LTreeData:= Sender.GetNodeData(Node);
      CellText:= LTreeData^.Fields[Column];
    end;
end;

procedure TForm2.VirtualTreeNewText(Sender: TBaseVirtualTree;
  Node: PVirtualNode; Column: TColumnIndex; NewText: string);
var
  LTreeData: PTreeData;
begin
  LTreeData:= Sender.GetNodeData(Node);
  LTreeData^.Fields[Column]:= NewText;
end;

end.

和EditorLink单位

unit EditorLink;

interface

uses
  Classes, SysUtils, Forms, Controls, Graphics, Dialogs,
  VirtualTrees, Messages, Windows, StdCtrls, Vcl.ExtCtrls;

type

  TStringEditLink = class(TInterfacedObject, IVTEditLink)
  private
    FEdit: TWinControl;
    FTree: TVirtualStringTree;
    FNode: PVirtualNode;
    FColumn: Integer;
    FStopping: Boolean;
  protected
    procedure EditKeyDown(Sender: TObject; var Key: Word; Shift: TShiftState);
  public
    destructor Destroy; override;
    function BeginEdit: Boolean; stdcall;
    function CancelEdit: Boolean; stdcall;
    function EndEdit: Boolean; stdcall;
    function GetBounds: TRect; stdcall;
    function PrepareEdit(Tree: TBaseVirtualTree; Node: PVirtualNode; Column: TColumnIndex): Boolean; stdcall;
    procedure ProcessMessage(var Message: TMessage); stdcall;
    procedure SetBounds(R: TRect); stdcall;
  end;

implementation

uses unit2;

destructor TStringEditLink.Destroy;
begin
  FEdit.Free;  //--> seems that due to this I get the access violation
  inherited;
end;

procedure TStringEditLink.EditKeyDown(Sender: TObject; var Key: Word; Shift: TShiftState);
begin
  case Key of
    VK_ESCAPE:
      begin
        FTree.CancelEditNode;
        Key := 0;
        FTree.setfocus;
      end;
    VK_RETURN:
      begin
       PostMessage(FTree.Handle, WM_KEYDOWN, VK_DOWN, 0);
       Key := 0;
       FTree.EndEditNode;
       FTree.setfocus;
      end;
  end; //case
end;

function TStringEditLink.BeginEdit: Boolean;
begin
  Result := not FStopping;
  if Result then
    begin
      FEdit.Show;
      FEdit.SetFocus;
    end;
end;

function TStringEditLink.CancelEdit: Boolean;
begin
  Result := True;
  FEdit.Hide;
end;

function TStringEditLink.EndEdit: Boolean;
var
  s: String;
begin
  Result := True;
  s := TComboBox(FEdit).Text;
  FTree.Text[FNode, FColumn] := s;

  FTree.InvalidateNode(FNode);
  FEdit.Hide;
  FTree.SetFocus;
end;

function TStringEditLink.GetBounds: TRect;
begin
  Result := FEdit.BoundsRect;
end;

function TStringEditLink.PrepareEdit(Tree: TBaseVirtualTree; Node: PVirtualNode; Column: TColumnIndex): Boolean;
var
  FCellText: String;
  FCellTextBounds: TRect;
  FCellFont: TFont;
begin
  Result := True;
  FTree := Tree as TVirtualStringTree;

  FNode := Node;
  FColumn := Column;

  FCellFont:= TFont.Create;
  FTree.GetTextInfo(FNode, FColumn, FCellFont, FCellTextBounds, FCellText);

  FEdit := TComboBox.Create(nil);
  with FEdit as TComboBox do
    begin
      Visible := False;
      Parent := Tree;
      Items.Add('Google');
      Items.Add('Yahoo');
      Items.Add('Altavista');
      OnKeyDown := EditKeyDown;
      Text:= FCellText;
    end;
end;

procedure TStringEditLink.ProcessMessage(var Message: TMessage);
begin
  FEdit.WindowProc(Message);
end;

procedure TStringEditLink.SetBounds(R: TRect);
var
  Dummy: Integer;
begin
  FTree.Header.Columns.GetColumnBounds(FColumn, Dummy, R.Right);
  FEdit.BoundsRect := R;
end;

end.

Answer 1

我没有 Lazarus，但它在 XE4 上似乎表现相同。

在我的 VST 安装中，位于 ./VirtualTreeviewV5.3.0/Demos/Advanced 中有一个 Editors.pas 文件，我在下面找到了析构函数。注意注释 casues issue #357:

destructor TPropertyEditLink.Destroy;
begin
  //FEdit.Free; casues issue #357. Fix:
  if FEdit.HandleAllocated then
    PostMessage(FEdit.Handle, CM_RELEASE, 0, 0);
  inherited;
end;

此外，FEdit.Free在其新创建之前在PrepareEdit方法中执行：

function TStringEditLink.PrepareEdit(Tree: TBaseVirtualTree; Node: PVirtualNode; Column: TColumnIndex): Boolean;
var
  FCellText: String;
  FCellTextBounds: TRect;
  FCellFont: TFont;
begin
  Result := True;
  FTree := Tree as TVirtualStringTree;

  FNode := Node;
  FColumn := Column;

  FEdit.Free;
  FEdit := nil;

  FCellFont:= TFont.Create;
  FTree.GetTextInfo(FNode, FColumn, FCellFont, FCellTextBounds, FCellText);

  FEdit := TComboBox.Create(nil);
  with FEdit as TComboBox do
  . . .

这解决了我的 XE4 和 XE7 安装中的 VK_ESC 和 VK_RETURN 问题。

问题 #357 似乎尚未解决：请参阅 - Used fix proposed in issue #361 to fix issue #357 (AV in advanced demo - PropertiesDemo form in XE3+)。我没有找到 #361 fix.

的证据

在编辑操作后单击未分配的节点时，我遇到了另一个问题。
在开始编辑之前检查 Click.HitNode 是否不是 nil 可以解决上述问题。

procedure TForm2.VirtualTreeClick(Sender: TObject);
var
  VT: TVirtualStringTree;
  Click: THitInfo;
begin
  VT:= Sender as TVirtualStringTree;
  VT.GetHitTestInfoAt(Mouse.CursorPos.X-VT.ClientOrigin.X, Mouse.CursorPos.Y-VT.ClientOrigin.Y, True, Click);

  if Assigned(Click.HitNode) then
    VT.EditNode(Click.HitNode,Click.HitColumn);
end;

另请注意，您在 EditorLink 单元中有一个循环引用：

uses Unit2;

Answer 2

你的代码的这个伪堆栈跟踪说明了这个问题：

FEdit.EditKeyDown()
  -- calls --
FTree.EndEditNode()  { or FTree.CancelEditNode }
  -- which calls --
TStringEditLink.Destroy()
  -- which calls --
FEdit.Free()

FEdit.EditKeyDown() 的事件处理程序中的代码在按键按下事件处理程序代码完成运行ning 之前释放 FEdit。因此访问冲突错误。

我们通过设置一个信号机制来处理这个问题，这样 TStringEditLink 可以在完成时向主窗体发出信号，主窗体可以运行销毁 TStringEditLink 的代码]（因为它首先创建了 TStringEditLink）。我们在主窗体中添加了一个 TTimer，并添加了一个属性来接收信号。 TTimer 关注属性。 TStringEditLink 组件有一个指向表单的指针，因此它可以设置属性.

unit Unit1;

interface

uses
  Winapi.Windows, Winapi.Messages, System.SysUtils, System.Variants, System.Classes, Vcl.Graphics,
  Vcl.Controls, Vcl.Forms, Vcl.Dialogs, Vcl.ExtCtrls, VirtualTrees;

type
  TEditorAction = (eaCancel, eaAccept, eaNotSet);

  TForm1 = class(TForm)
    vstTree: TVirtualStringTree;
    procedure vstTreeCreateEditor(Sender: TBaseVirtualTree; Node: PVirtualNode; Column: TColumnIndex; out EditLink: IVTEditLink);
    procedure DoWatchTreeEditorTimer(Sender: TObject);
    procedure FormCreate(Sender: TObject);
    procedure FormDestroy(Sender: TObject);
  private
    FEndEditTimer: TTimer;
    FEditorAction: TEditorAction;
    procedure SetEditorAction(const Value: TEditorAction);
  public
    property EditorAction: TEditorAction read FEditorAction write SetEditorAction;
  end;

  TPropertyEdit = class(TInterfacedObject, IVTEditLink)
    procedure EditKeyDown(Sender: TObject; var Key: Word; Shift: TShiftState);
  private
    FEdit: TWinControl;
    FTree: TVirtualStringTree;
    FNode: PVirtualNode;
    FColumn: Integer;
  public
    FForm: TForm1;
    destructor Destroy; override;
    function BeginEdit: Boolean; stdcall;
    function CancelEdit: Boolean; stdcall;
    function EndEdit: Boolean; stdcall;
    function GetBounds: TRect; stdcall;
    function PrepareEdit(Tree: TBaseVirtualTree; Node: PVirtualNode; Column: TColumnIndex): Boolean; stdcall;
    procedure ProcessMessage(var Message: TMessage); stdcall;
    procedure SetBounds(R: TRect); stdcall;
  end;

var
  Form1: TForm1;

implementation

{$R *.dfm}

{ TForm1 }

procedure TForm1.FormCreate(Sender: TObject);
begin
  FEndEditTimer := TTimer.Create(nil);
  FEndEditTimer.Enabled := False;
  FEndEditTimer.Interval := 100;
  FEndEditTimer.OnTimer := DoWatchTreeEditorTimer;
end;

procedure TForm1.FormDestroy(Sender: TObject);
begin
  FreeAndNil(FEndEditTimer);
end;

procedure TForm1.vstTreeCreateEditor(Sender: TBaseVirtualTree; Node: PVirtualNode; Column: TColumnIndex; out EditLink: IVTEditLink);
begin
  EditLink := TPropertyEdit.Create;
  TPropertyEdit(EditLink).FForm := Self; { lets us signal the form when the editor needs to be destroyed }
  FEditorAction := eaNotSet;
end;

procedure TForm1.SetEditorAction(const Value: TEditorAction);
begin
  if FEditorAction <> Value then
  begin
    FEditorAction := Value;
    FEndEditTimer.Enabled := True;
  end;
end;

procedure TForm1.DoWatchTreeEditorTimer(Sender: TObject);
begin
  FEndEditTimer.Enabled := False;
  Application.ProcessMessages;
  case FEditorAction of
    eaCancel:
      begin
        vstTree.CancelEditNode;
        vstTree.SetFocus;
      end;
    eaAccept:
      begin
        vstTree.EndEditNode;
        vstTree.SetFocus;
      end;
  end;
end;

{ TPropertyEdit }

function TPropertyEdit.BeginEdit: Boolean;
begin
  Result := True;
  FEdit.Show;
end;

function TPropertyEdit.CancelEdit: Boolean;
begin
  Result := True;
  FEdit.Hide;
  FForm.FEditorAction := eaCancel;
end;

destructor TPropertyEdit.Destroy;
begin
  if FEdit <> nil then
    FreeAndNil(FEdit);
  inherited;
end;

procedure TPropertyEdit.EditKeyDown(Sender: TObject; var Key: Word; Shift: TShiftState);
begin
  case Key of
    VK_ESCAPE:
      begin
        Key := Word(0); { some versions of Delphi throw random A/V errors if '0' is not cast as a Word() }
        FForm.EditorAction := eaCancel;
      end;
    VK_RETURN:
      begin
        Key := Word(0); { some versions of Delphi throw random A/V errors if '0' is not cast as a Word() }
        FForm.EditorAction := eaAccept
      end;
  end;
end;

function TPropertyEdit.EndEdit: Boolean;
begin
  Result := True;
  { Do something with the value provided by the user }
  FEdit.Hide;
  FForm.EditorAction := eaAccept;
end;

function TPropertyEdit.GetBounds: TRect;
begin
  Result := FEdit.BoundsRect;
end;

function TPropertyEdit.PrepareEdit(Tree: TBaseVirtualTree; Node: PVirtualNode; Column: TColumnIndex): Boolean;
begin
  Result := True;
  FTree := Tree as TVirtualStringTree;
  FNode := Node;
  FColumn := Column;
  { Setup the editor for user }
  FEdit := TSomeWinControl.Create(nil);
  FEdit.Properties := Values;
  { Capture keystrokes }
  FEdit.OnKeyDown := EditKeyDown;
end;

procedure TPropertyEdit.ProcessMessage(var Message: TMessage);
begin
  FEdit.WindowProc(Message);
end;

procedure TPropertyEdit.SetBounds(R: TRect);
var
  Dummy: Integer;
begin
  FTree.Header.Columns.GetColumnBounds(FColumn, Dummy, R.Right);
  FEdit.BoundsRect := R;
end;

end.

我们的代码做了很多额外的事情，所以上面的代码是 copy/paste 演示如何克服竞争条件的基本部分。它未经测试，但应该能为您指明正确的方向。

Answer 3

在HeidiSql源代码中有一个很好的例子可以避免这个错误。稍作改动的代码是：

procedure TBaseEditorLink.TempWindowProc(var Message: TMessage);
begin
  case Message.Msg of
    WM_CHAR: //Catch hotkeys
      if not (TWMChar(Message).CharCode = VK_TAB) then FOldWindowProc(Message);
    WM_GETDLGCODE: //"WantTabs" mode for main control
      Message.Result := Message.Result or DLGC_WANTARROWS or DLGC_WANTALLKEYS or DLGC_WANTTAB;
    else
      begin
        try
          FOldWindowProc(Message);
        except
          on E : EAccessViolation do; //EAccessViolation occurring in some cases
          on E : Exception do raise;
        end;
      end;
  end;
end;

Answer 4

一个解决方案也是释放以前创建的控件。

function TStringEditLink.PrepareEdit(Tree: TBaseVirtualTree; Node: PVirtualNode; Column: TColumnIndex): Boolean;
var
  FCellText: String;
  FCellTextBounds: TRect;
  FCellFont: TFont;
  i: Integer;
  Item: TControl;
begin
  Result := True;
  FTree := Tree as TVirtualStringTree;

  FNode := Node;
  FColumn := Column;

  FCellFont:= TFont.Create;
  FTree.GetTextInfo(FNode, FColumn, FCellFont, FCellTextBounds, FCellText);

  //----->> free previuous created control <<----------
  for i := (FTree.ControlCount - 1) downto 0 do
    begin
      Item := FTree.controls[i];
      if assigned(item) then
        begin
          if item is TComboBox then FreeAndNil(item);
        end;
    end;
  //---------------------------------------------------

  FEdit := TComboBox.Create(nil);
  with FEdit as TComboBox do
    begin
      Visible := False;
      Parent := Tree;
      Items.Add('Google');
      Items.Add('Yahoo');
      Items.Add('Altavista');
      OnKeyDown := EditKeyDown;
      Text:= FCellText;
    end;
end;

Answer 5

我最后使用的解决方案如下：

TBasePanel = class(TPanel)
  private
    procedure CMRelease(var Message: TMessage); message CM_RELEASE;
  protected
  public
    procedure Release; virtual;
  end;

TStringEditLink = class(TInterfacedObject, IVTEditLink)
  private
    FBasePanel: TBasePanel;
    ...
  protected
    procedure EditKeyDown(Sender: TObject; var Key: Word; Shift: TShiftState);
  public
    destructor Destroy; override;
    function BeginEdit: Boolean; stdcall;
    function CancelEdit: Boolean; stdcall;
    function EndEdit: Boolean; stdcall;
    function GetBounds: TRect; stdcall;
    function PrepareEdit(Tree: TBaseVirtualTree; Node: PVirtualNode; Column: TColumnIndex): Boolean; stdcall;
    procedure ProcessMessage(var Message: TMessage); stdcall;
    procedure SetBounds(R: TRect); stdcall;
  end;

implementation

procedure TBasePanel.CMRelease(var Message: TMessage);
begin
  Free;
end;

procedure TBasePanel.Release;
begin
  if HandleAllocated then
    PostMessage(Handle, CM_RELEASE, 0, 0);
end;

destructor TStringEditLink.Destroy;
begin
  if Assigned(FBasePanel) then FBasePanel.Release;
  inherited;
end;

FBasePanel 应用作 owner 和 parent，以便同时显示尽可能多的组件编辑器。

TStringEditLink 被销毁后访问冲突（TVirtualStringTree）- Lazarus 示例

Access violation after TStringEditLink get destroyed (TVirtualStringTree) - Lazarus example

delphi

virtualtreeview

tvirtualstringtree